Trivia: The plot of the movie is similar to Groundhog Day which is something that Carter mentions to Tree at the end of the movie. Tree's roommate's name is Laurie Spengler, which is a reference to Egon Spengler, played by Harold Ramis in Ghostbusters. Harold Ramis co-wrote and directed Groundhog Day.
Trivia: There actually is an in-universe explanation for why Tree got stuck in a time-loop. However, director Christopher Landon opted to omit it from the finished film. Partially because it could be used in a potential sequel, and partially because it wasn't necessary for the narrative. Landon has hinted that the upcoming sequel, "Happy Death Day 2U," will finally reveal the explanation.TedStixon
Trivia: The killer's mask was designed by Tony Gardner. If that name sounds familiar, you're probably a big horror fan. Aside from the killer's mask in "Happy Death Day," Gardner also helped design the final look of "Ghostface" seen in the"Scream" franchise (albeit loosely based on an earlier design), worked on a number of cult-films including "Darkman, "Hocus Pocus" and the "Evil Dead" sequels, and has worked as the main effects supervisor on a number of the "Chucky/Child's Play" films.TedStixon
Tree Gelbman: It's been so much worse.
Tree Gelbman: All of this running and hiding has made me so miserable.
Tree Gelbman: And I think I finally figured it out.
Tree Gelbman: For me, it took something, like, totally crazy, but.
Tree Gelbman: But I'm here.
Tree Gelbman: And I love you.
Tree Gelbman: And I'm so, so sorry that I hurt you.